#-*- coding:utf-8 -*-
numb1=input("students mark appeared:")

#print numb1
if numb1>=90 and numb1<=100:
	print 'A'
elif numb1>60 and numb1<90:
	print 'B'
elif numb1<60 and numb1>0:
	print 'C'
elif numb1>100 and numb1<0:
	print "error"
